One issue left from the list of past mistakes: what kind of game engine(s) will they use?

Given that their last mostly home build engine left them with an unpatchable game, required huge compilation times (if you believe in this) and due to a lack of modularity behaved unpredictably on a large scale for every small scale change in the code - among other things - the choice of engine is probably my main concern regarding Project RPB.

On the other hand, it is not likely that they will repeat the same mistake twice.